The present invention relates to a developing unit of the type developing a latent image formed on an image carrier by depositing a developing liquid, which consists of a carrier liquid and a developing substance, and a copier, facsimile apparatus, printer or similar image forming apparatus including the same.
A developing unit for use in an image forming apparatus uses either one of a dry powdery developer or a developing liquid. Generally, a developing unit using a developing liquid includes a developing roller rotatable while carrying the liquid thereon. A voltage for development is applied to the developing roller to thereby form an electric field between the roller and an image carrier.
The problem with a developing unit of the type described is that a toner image formed thereby is sometimes irregular. By a series of researches and experiments, I found that irregular development was ascribable to the unstable strength of the electric field. Further, I found that in a so-called contact type developing unit that develops the latent image with the developing roller contacting the image carrier, irregularities on the surface of the roller cause fine irregularities to appear on the surface of the developing liquid deposited on the roller, also making development irregular.
It is therefore an object of the present invention to provide a developing unit using a developing liquid and capable of reducing irregular development, and an image forming apparatus including the same.
In accordance with the present invention, a developing unit for developing a latent image formed on an image carrier with a developing liquid consisting of a carrier liquid and a developing substance includes a developing roller including a roller portion and configured to rotate while carrying the developing liquid on the roller portion. A voltage applying device applies a voltage to the roller portion to thereby form an electric field for development between the roller portion and the image carrier. The electric field transfers the developing liquid deposited on the roller portion to a latent image formed on the image carrier. The roller portion has a volume resistivity ranging from 0 xcexa9xc2x7cm to 107 xcexa9xc2x7cm.
Further, in accordance with the present invention, an image forming apparatus includes an image carrier configured to carry a latent image thereon. A developing unit develops the latent image by depositing a developing liquid, which consists of a carrier liquid and a developing substance, on the latent image. A developing roller includes a roller portion and rotates while carrying the developing liquid on the roller portion. A voltage applying device applies a voltage to the roller portion to thereby form an electric field for development between the roller portion and the image carrier. The electric field transfers the developing liquid from the roller portion to the latent image formed on the image carrier. The roller portion has a volume resistivity ranging from 0 xcexa9xc2x7cm to 107 xcexa9xc2x7cm.